Magnetic properties of disordered oxides with iron and manganese ions

Magnetic properties of disordered oxides involving oxide glasses have been investigated. Spin glass-like transition is observed for Fe₂O₃–TeO₂ and MnO–TeO₂ glasses in temperature dependence of dc susceptibility, although magnetic transition does not take place for MnO–TeO₂ glasses with low concentration of manganese ion above 2 K at least. The mechanism of magnetic transition observed for Fe₂O₃–TeO₂ glasses is discussed on the basis of dc susceptibility obtained under conditions of field cooling and zero field cooling, magnetic field dependence of magnetization at low temperatures, and frequency dependence of spin-freezing temperature derived from temperature dependence of ac susceptibility. Magnetic properties of disordered ZnFe₂O₄ thin film prepared by a radio frequency sputtering method have been also studied. The disordered ZnFe₂O₄ thin film exhibits ferrimagnetic behavior with high magnetization even at room temperature. At the same time, the thin film shows spin-freezing at around 320 K. Temperature dependence of nonlinear susceptibility leads to a conclusion that this transition is explainable in terms of superparamagnetism with magnetic interaction among clusters.     

Integral Representations of the Wilson Polynomials and the Continuous Dual Hahn Polynomials

We give representations of the Wilson polynomials and the continuous dual Hahn polynomials in terms of multidimensional generalizations of Barnes type integrals. Motivation is to study the Barnes type integrals from the viewpoint of the de Rham theory and holonomic systems.     

Enhanced magnetization and ferrimagnetic behavior of normal spinel ZnFe2O4 thin film irradiated with femtosecond laser

We report on spatially selective change of magnetism from paramagnetic to ferrimagnetic-like behaviors in normal spinel ZnFe₂O₄ thin film under irradiation with 780 nm femtosecond laser pulses. The distribution of Zn²⁺ and Fe³⁺ ions in the irradiated region on the film surface becomes disordered because of local heating to high temperatures, and the metastable phase of ZnFe₂O₄ is frozen in by the rapid quenching after irradiation, resulting in the formation of the ferrimagnetic phase. The ferrimagnetic phase reverts to the paramagnetic state by annealing at 800°C. The present technique is useful for two-dimensional patterning of magnetic thin films.     

Heavily carbon-doped p-type InGaAs by MOMBE

Carbon-doped In_xGa_1−xAs layers (x=0−0.96) were grown by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG), solid arsenic (As₄) and solid indium (In) as sources of Ga, As and In, respectively. The carrier concentration is strongly affected by growth temperature and indium beam flux. Heavy p-type doping is obtained for smaller In compositions. The hole concentration decreases with the indium composition from 0 to 0.8, and then the conductivity type changes from p to n at x=0.8. Hole concentrations of 1.0×10¹⁹ and 1.2×10¹⁸ cm^-3 are obtained for x=0.3 and 0.54, respectively. These values are significantly higher than those reported on carbon-doped In_xGa_1−xAs by MBE. Preliminary results on carbon-doped GaAs/In_xGa_1−xAs strained layer superlattices are also discussed.     

Intersection Numbers of Twisted Cycles and the Correlation Functions of the Conformal Field Theory

 The coefficients of the four-point correlation functions calculated by Dotsenko-Fateev are interpreted naturally in terms of the intersection numbers of twisted (or loaded) cycles. This is an answer to the long standing problem of clarifying the meaning of such coefficients appearing in correlation functions. Received: 8 March 2002 / Accepted: 25 September 2002 Published online: 8 January 2003 Communicated by L. Takhtajan     

MnTaO2N: Polar LiNbO3‐type Oxynitride with a Helical Spin Order

The synthesis, structure, and magnetic properties of a polar and magnetic oxynitride MnTaO₂N are reported. High‐pressure synthesis at 6 GPa and 1400 °C allows for the stabilization of a high‐density structure containing middle‐to‐late transition metals. Synchrotron X‐ray and neutron diffraction studies revealed that MnTaO₂N adopts the LiNbO₃‐type structure, with a random distribution of O^2? and N^3? anions. MnTaO₂N with an “orbital‐inactive” Mn²⁺ ion (d⁵; S=5/2) exhibits a nontrivial helical spin order at 25 K with a propagation vector of [0,0,δ] (δ≈0.3), which is different from the conventional G‐type order observed in other orbital‐inactive perovskite oxides and LiNbO₃‐type oxides. This result suggests the presence of strong frustration because of the heavily tilted MnO₄N₂ octahedral network combined with the mixed O^2?/N^3? species that results in a distribution of (super)‐superexchange interactions.     

Gauging away the electron–electron interaction by the local phase of complex wave functions in two-electron systems

The electron–electron interaction is eliminated in the expectation values of the electronic Hamiltonian for two-electron systems. The part of the Hamiltonian referring to the repulsive interaction is gauged away by the local phase of the complex wave functions, much like a gauge field transformation, thereby leading to a one-electron Hamiltonian. Despite the appearance of complex wave functions, the expectation values of the total momentum operator vanish and Löwdin’s criterion holds for the stationary states.     

The electronic structures of polyacene and polyphenanthrene

The electronic structures of polyacene (PA) and its geometrical isomer, polyphenanthrene (PP) are studied on the basis of the one-dimensional tight-binding SCF-CO (self consistent field-crystal orbital) method. PA and PP can also be regarded as the laddered trans-polyacetylene and cis-polyacetylene, respectively. The geometry of each polymer is optimized from the energetic point of view. Although being energetically less stable than PP, PA has a small band gap and, furthermore, turns out to have a considerable dopant-philic nature. Hence PA will be a promising candidate as a new electrically conductive material because of its “intrinsically” metallic nature and thermal stability.     

Jackson’s integral of the Hurwitz zeta function

We give a Jacksonq-integral analogue of Euler’s logarithmic sine integral established in 1769 from several points of view, specifically from the one relating to the Hurwitz zeta function.     

Real-time Optical Wavelet-Transform with Positive and Negative Signals

An opto-electronic hybrid system that is based on the joint transform correlator (JTC) is suggested for the implementation of real-time wavelet transform. Holographic encoding of both the object signal and wavelet function enables the JTC-based real-time correlator to execute the optical wavelet transformation involving positive and negative values. We suggest an interferometric method to retain the information about the polarity of the final wavelet transform. The principle of this method is verified by experiments.Presented at 1996 International Topical Meeting on Optical Computing (OC ‘96), April 21-25, Sendai, Japan.